System and method for testing radio frequency wireless signal transceivers using wireless test signals

ABSTRACT

A method of facilitating wireless testing of multiple radio frequency (RF) signal transceiver devices under test (DUTs). Using multiple antennas within a shielded enclosure containing the DUTs, multiple wireless RF test signals radiated to the DUTs can have their respective signal phases controlled to maximize the direct-coupled signals to their respective intended DUTs while minimizing the cross-coupled signals. Additionally, the wireless RF test signals radiated to the DUTs can have their respective signal magnitudes controlled to normalize the direct-coupled signals to their respective intended DUTs while still sufficiently reducing the cross-coupled signals. As a result, compensation is provided for the multipath signal environment within the shielded enclosure, thereby simulating wired test signal paths during wireless testing of the DUTs.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 13/839,162, filed Mar. 15, 2013, and entitled “System andMethod for Testing Radio Frequency Wireless Signal Transceivers UsingWireless Test Signals”, and a continuation-in-part of U.S. patentapplication Ser. No. 13/839,583, filed Mar. 15, 2013, and entitled“System and Method for Testing Radio Frequency Wireless SignalTransceivers Using Wireless Test Signals”, the contents of both of whichare incorporated herein by reference.

BACKGROUND

The present invention relates to testing of radio frequency (RF)wireless signal transceivers, and in particular, to testing such deviceswithout a need for RF signal cables for conveyance of RF test signals.

Many of today's electronic devices use wireless technologies for bothconnectivity and communications purposes. Because wireless devicestransmit and receive electromagnetic energy, and because two or morewireless devices have the potential of interfering with the operationsof one another by virtue of their signal frequencies and power spectraldensities, these devices and their wireless technologies must adhere tovarious wireless technology standard specifications.

When designing such devices, engineers take extraordinary care to ensurethat such devices will meet or exceed each of their included wirelesstechnology prescribed standard-based specifications. Furthermore, whenthese devices are later being manufactured in quantity, they are testedto ensure that manufacturing defects will not cause improper operation,including their adherence to the included wireless technologystandard-based specifications.

For testing these devices following their manufacture and assembly,current wireless device test systems (“testers”) employ a subsystem foranalyzing signals received from each device. Such subsystems typicallyinclude at least a vector signal generator (VSG) for providing thesource signals to be transmitted to the device, and a vector signalanalyzer (VSA) for analyzing signals produced by the device. Theproduction of test signals by the VSG and signal analyses performed bythe VSA are generally programmable so as to allow each to be used fortesting a variety of devices for adherence to a variety of wirelesstechnology standards with differing frequency ranges, bandwidths andsignal modulation characteristics.

Calibration and performance verification testing of a device under test(DUT) are typically done using electrically conductive signal paths,such as RF cables, rather than wireless signal paths, by which a DUT andtester communicate via electromagnetic radiation. Accordingly, thesignals between the tester and DUT are conveyed via the conductivesignal path rather than being radiated through ambient space. Using suchconductive signal paths helps to ensure repeatability and consistency ofmeasurements, and eliminates positioning and orientation of the DUT as afactor in signal conveyance (transmission and reception).

In the case of a multiple input, multiple output (MIMO) DUT, a signalpath must be provided, in some form, for each input/output connection ofthe DUT. For example, for a MIMO device intended to operate with threeantennas, three conductive signal paths, e.g., cables and connections,must be provided for testing.

However, using conductive signal paths significantly impacts the timeneeded for testing each DUT due to the need for physically connectingand disconnecting the cables between the DUT and tester. Further, in thecase of a MIMO DUT, multiple such connecting and disconnecting actionsmust be performed, both at the beginning and termination of testing.Further, since the signals being conveyed during testing are notradiated via the ambient space, as they would be in the normallyintended use, and the antenna assemblies for the DUT are not in useduring such testing, such testing does not simulate real world operationand any performance characteristics attributable to the antennas are notreflected in the test results.

As an alternative, testing could be done using test signals conveyed viaelectromagnetic radiation rather than electrical conduction via cables.This would have the benefit of requiring no connecting and disconnectingof test cables, thereby reducing the test time associated with suchconnections and disconnections. However, the “channel” in which theradiated signals and receiver antennas exist, i.e., the ambient spacethrough which the test signals are radiated and received, is inherentlyprone to signal interference and errors due to other electromagneticsignals originating elsewhere and permeating the ambient space. Suchsignals will be received by the DUT antennas and can include multipathsignals from each interfering signal source due to signal reflections.Accordingly, the “condition” of the “channel” will typically be poorcompared to using individual conductive signal paths, e.g., cables, foreach antenna connection.

One way to prevent, or at least significantly reduce, interference fromsuch extraneous signals, is to isolate the radiated signal interface forthe DUT and tester using a shielded enclosure. However, such enclosureshave typically not produced comparable measurement accuracy andrepeatability. This is particularly true for enclosures that are smallerthan the smallest anechoic chambers. Additionally, such enclosures tendto be sensitive to the positioning and orientation of the DUT, as wellas to constructive and destructive interference of multipath signalsproduced within such enclosures.

Accordingly, it would be desirable to have systems and methods fortesting wireless signal transceivers, and particularly wireless MIMOsignal transceivers, in which radiated electromagnetic test signals canbe used, thereby simulating real world system operation as well asavoiding test time otherwise necessary for connecting and disconnectingtest cabling, while maintaining test repeatability and accuracy byavoiding interfering signals due to externally generated signals andmultipath signal effects.

SUMMARY

In accordance with the presently claimed invention, a method providesfor facilitating wireless testing of multiple radio frequency (RF)signal transceiver devices under test (DUTs). Using multiple antennaswithin a shielded enclosure containing the DUTs, multiple wireless RFtest signals radiated to the DUTs can have their respective signalphases controlled to maximize the direct-coupled signals to theirrespective intended DUTs while minimizing the cross-coupled signals.Additionally, the wireless RF test signals radiated to the DUTs can havetheir respective signal magnitudes controlled to normalize thedirect-coupled signals to their respective intended DUTs while stillsufficiently reducing the cross-coupled signals. As a result,compensation is provided for the multipath signal environment within theshielded enclosure, thereby simulating wired test signal paths duringwireless testing of the DUTs.

In accordance with one embodiment of the presently claimed invention, amethod of facilitating wireless testing of a plurality of radiofrequency (RF) signal transceiver devices under test (DUTs) includes:

providing at least first and second wired RF test signals havingcorresponding at least first and second wired RF test signal phases;

controlling the at least first and second wired RF test signal phases toprovide corresponding at least first and second controlled RF signals;

transmitting, via a plurality of antennas disposed at least partiallywithin an interior region of a structure, the at least first and secondcontrolled RF signals for reception by at least first and second DUTs,respectively, disposed within the interior region, wherein the structuredefines the interior region and an exterior region, and is configured tosubstantially isolate the interior region from electromagnetic radiationoriginating from the exterior region;

receiving corresponding at least first and second signals from the atleast first and second DUTs indicative, respectively, of at least

-   -   as received by the first DUT, a first power level of one or more        signals related to the first controlled RF signal and a second        power level of one or more signals not related to the first        controlled RF signal, and    -   as received by the second DUT, a third power level of one or        more signals related to the second controlled RF signal and a        fourth power level of one or more signals not related to the        second controlled RF signal; and

repeating the controlling of the at least first and second wired RF testsignal phases until the first and third power levels exceed the thirdand fourth power levels by a minimum amount.

In accordance with another embodiment of the presently claimedinvention, a method of facilitating wireless testing of a plurality ofradio frequency (RF) signal transceiver devices under test (DUTs)includes:

providing at least first and second wired RF test signals havingcorresponding at least first and second wired RF test signal phases;

controlling the at least first and second wired RF test signal phases toprovide corresponding at least first and second controlled RF signals;

transmitting, via a plurality of antennas disposed at least partiallywithin an interior region of a structure, the at least first and secondcontrolled RF signals for reception by at least first and second DUTs,respectively, disposed within the interior region, wherein

-   -   the structure defines the interior region and an exterior        region, and is configured to substantially isolate the interior        region from electromagnetic radiation originating from the        exterior region, and    -   the plurality of antennas and at least a portion of the interior        region together define at least a portion of a wireless        communication channel via which at least first and second        pluralities of controlled RF signal components related to the at        least first and second controlled RF signals, respectively,        propagate for reception by the at least first and second DUTs,        respectively;

receiving corresponding at least first and second signals from the atleast first and second DUTs indicative, respectively, of at least

-   -   as received by the first DUT, a first power level of the first        plurality of controlled RF signal components and a second power        level of a plurality of controlled RF signal components other        than the first plurality of controlled RF signal components, and    -   as received by the second DUT, a third power level of the second        plurality of controlled RF signal components and a fourth power        level of another plurality of controlled RF signal components        other than the second plurality of controlled RF signal        components; and

repeating the controlling of the at least first and second wired RF testsignal phases until the first and third power levels exceed the thirdand fourth power levels by a minimum amount.

In accordance with another embodiment of the presently claimedinvention, a method of facilitating wireless testing of a plurality ofradio frequency (RF) signal transceiver devices under test (DUTs)includes:

providing at least first and second wired RF test signals havingcorresponding at least first and second wired RF test signal phases;

controlling the at least first and second wired RF test signal phases toprovide corresponding at least first and second controlled RF signals;

transmitting, via a plurality of antennas disposed at least partiallywithin an interior region of a structure, the at least first and secondcontrolled RF signals for reception by at least first and second DUTsdisposed within the interior region, wherein

-   -   the structure defines the interior region and an exterior        region, and is configured to substantially isolate the interior        region from electromagnetic radiation originating from the        exterior region, and    -   the plurality of antennas and at least a portion of the interior        region together define at least a portion of a wireless        communication channel characterized by a wireless communication        channel matrix H having a plurality of wireless communication        channel coefficients hij, including direct-coupled coefficients,        where i=j, and cross-coupled coefficients, where i≠j;

receiving corresponding at least first and second signals from the atleast first and second DUTs indicative of corresponding at least firstand second power levels of the at least first and second controlled RFsignals received by the at least first and second DUTs and related tothe plurality of wireless communication channel coefficients; and

repeating the controlling of the at least first and second wired RF testsignal phases until the direct-coupled coefficients are greater than thecross-coupled coefficients by a minimum amount.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a typical operating and possible testing environment fora wireless signal transceiver.

FIG. 2 depicts a testing environment for a wireless signal transceiverusing a conductive test signal path.

FIG. 3 depicts a testing environment for a MIMO wireless signaltransceiver using conductive signal paths and a channel model for suchtesting environment.

FIG. 4 depicts a testing environment for a MIMO wireless signaltransceiver using radiated electromagnetic signals a channel model forsuch testing environment.

FIG. 5 depicts a testing environment in accordance with exemplaryembodiments in which a MIMO DUT can be tested using radiatedelectromagnetic test signals.

FIG. 6 depicts a testing environment in which a DUT is tested usingradiated electromagnetic test signals within a shielded enclosure.

FIGS. 7 and 8 depict exemplary embodiments of testing environments inwhich a wireless DUT is tested using radiated electromagnetic testsignals in a shielded enclosure with reduced multipath signal effects.

FIG. 9 depicts a physical representation of a shielded enclosure inaccordance with an exemplary embodiment for use in the testingenvironments of FIGS. 7 and 8.

FIG. 10 depicts a testing environment in accordance with exemplaryembodiments in which a DUT can be tested using radiated electromagnetictest signals.

FIG. 11 depicts another testing environment in accordance with exemplaryembodiments in which a DUT can be tested using radiated electromagnetictest signals.

FIG. 12 depicts an exemplary algorithm for testing a DUT using thetesting environment of FIG. 11.

FIG. 13 depicts another testing environment in accordance with exemplaryembodiments in which a DUT can be tested using radiated electromagnetictest signals.

FIG. 14 depicts an exemplary algorithm for testing a DUT using thetesting environment of FIG. 13.

FIG. 15 depicts another testing environment in accordance with exemplaryembodiments in which a DUT can be tested using radiated electromagnetictest signals.

FIG. 16 depicts an exemplary algorithm for testing a DUT using thetesting environment of FIG. 15.

FIG. 17 depicts a test signal transmitted by a DUT over a definedfrequency range prior to compensation in accordance with exemplaryembodiments.

FIG. 18 depicts the swept test signal of FIG. 17 prior to and followingcompensation in accordance with exemplary embodiments, along withexemplary phase shift values for the testing environments of FIGS. 10,11, 13 and 15.

FIG. 19 depicts an exemplary algorithm for performing compensation asdepicted in FIG. 18.

FIG. 20 depicts another testing environment for testing a wireless DUTwith compensation using multiple test signal phase shifts in accordancewith exemplary embodiments.

FIG. 21 depicts the testing environment of FIG. 20 with the addition oftest signal gain adjustments for compensating in accordance withadditional exemplary embodiments.

DETAILED DESCRIPTION

The following detailed description is of example embodiments of thepresently claimed invention with references to the accompanyingdrawings. Such description is intended to be illustrative and notlimiting with respect to the scope of the present invention. Suchembodiments are described in sufficient detail to enable one of ordinaryskill in the art to practice the subject invention, and it will beunderstood that other embodiments may be practiced with some variationswithout departing from the spirit or scope of the subject invention.

Throughout the present disclosure, absent a clear indication to thecontrary from the context, it will be understood that individual circuitelements as described may be singular or plural in number. For example,the terms “circuit” and “circuitry” may include either a singlecomponent or a plurality of components, which are either active and/orpassive and are connected or otherwise coupled together (e.g., as one ormore integrated circuit chips) to provide the described function.Additionally, the term “signal” may refer to one or more currents, oneor more voltages, or a data signal. Within the drawings, like or relatedelements will have like or related alpha, numeric or alphanumericdesignators. Further, while the present invention has been discussed inthe context of implementations using discrete electronic circuitry(preferably in the form of one or more integrated circuit chips), thefunctions of any part of such circuitry may alternatively be implementedusing one or more appropriately programmed processors, depending uponthe signal frequencies or data rates to be processed. Moreover, to theextent that the figures illustrate diagrams of the functional blocks ofvarious embodiments, the functional blocks are not necessarilyindicative of the division between hardware circuitry.

Referring to FIG. 1, a typical operating environment, and ideal testingenvironment for a wireless signal transceiver (at least in terms ofsimulating real world operation), would have the tester 100 and DUT 200communicate wirelessly. Typically, some form of test controller 10,(e.g., a personal computer) will also be used to exchange testingcommands and data via wired signal interfaces 11 a, 11 b with the tester100 and DUT 200. The tester 100 and DUT 200 each have one (or more forMIMO devices) respective antennas 102, 202, which connect by way ofconductive signal connectors 104, 204 (e.g., coaxial cable connections,many types of which are well known in the art). Test signals (source andresponse) are conveyed wirelessly between the tester 100 and DUT 200 viathe antennas 102, 202. For example, during a transmit (TX) test of theDUT 200, electromagnetic signals 203 are radiated from the DUT antenna202. Depending upon the directivity of the antenna emission pattern,this signal 203 will radiate in numerous directions, resulting in anincident signal component 203 i and reflected signal components 203 rbeing received by the tester antenna 102. As discussed above, thesereflected signal components 203 r, often the products of multipathsignal effects as well as other electromagnetic signals originatingelsewhere (not shown), result in constructive and destructive signalinterference, thereby preventing reliable and repeatable signalreception and testing results.

Referring to FIG. 2, to avoid such unreliable testing results, aconductive signal path, such as a RF coaxial cable 106, is used toconnect the antenna connectors 104, 204 of the tester 100 and DUT 200 toprovide a consistent, reliable and repeatable electrically conductivesignal path for conveyance of the test signals between the tester 100and DUT 200. As discussed above, however, this increases the overalltest time due to the time needed for connecting and disconnecting thecable 106 before and after testing.

Referring to FIG. 3, the additional test time for connecting anddisconnecting test cabling becomes even longer when testing a MIMO DUT200 a. In such cases, multiple test cables 106 are needed to connectcorresponding tester 104 and DUT 204 connectors to enable conveyance ofthe RF test signals from the RF signal sources 110 (e.g., VSGs) withinthe tester 100 a for reception by the RF signal receivers 210 within theDUT 200 a. For example, in a typical testing environment, the tester fortesting MIMO devices will have one or more VSGs 110 a, 110 b, . . . ,110 n providing corresponding one or more RF test signals 111 a, 111 b,. . . , 111 n (e.g., packet data signals having variable signal power,packet contents and data rates). Their corresponding test cables 106 a,106 b, . . . , 106 n, connected via respective tester 104 a, 104 b, 104n and DUT 204 a, 204 b, . . . , 204 n connectors, convey these signalsto provide the received RF test signals 211 a, 211 b, . . . , 211 n forthe corresponding RF signal receivers 210 a, 210 b, . . . , 210 n withinthe DUT 200 a. Accordingly, the additional test time required forconnecting and disconnecting these test cables 106 can be increased by afactor n corresponding to the number of test cables 106.

As discussed above, using test cables for connecting the tester 100 aand DUT 200 a does have the advantage of providing consistent, reliable,and repeatable test connections. As is well known in the art, these testconnections 107 can be modeled as a signal channel H characterized by adiagonal matrix 20, where the diagonal matrix elements 22 correspond tothe direct-coupled coefficients h₁₁, h₂₂, . . . , h_(nn) (h_(ij), wherei=j) for the respective signal channel characteristics (e.g., signalpath conductivities or losses for the respective test cables 106).

Referring to FIG. 4, in accordance with one or more exemplaryembodiments, the conductive, or wired, channel 107 (FIG. 3) is replacedby a wireless channel 107 a corresponding to a wireless signal interface106 a between the tester 100 a and DUT 200 a. As discussed above, thetester 100 a and DUT 200 a communicate test signals 111, 211 viarespective arrays of antennas 102, 202. In this type of testenvironment, the signal channel 107 a is no longer represented by adiagonal matrix 20, but is instead represented by a matrix 20 a havingone or more non-zero cross-coupled coefficients 24 a, 24 b (h_(ij),where i≠j) off of the diagonal 22. As will be readily understood by oneskilled in the art, this is due to the multiple wireless signal pathsavailable in the channel 107 a. For example, unlike a cabled signalenvironment in which, ideally, each DUT connector 204 receives only thesignal from its corresponding tester connector 104. In this wirelesschannel 107 a, the first DUT antenna 202 a receives test signalsradiated by all of the tester antennas 102 a, 102 b, . . . , 102 n,e.g., corresponding to channel H matrix coefficients h₁₁, h₁₂, . . . ,and h_(1n).

In accordance with well known principles, the coefficients h of thechannel matrix H correspond to characteristics of the channel 107 aaffecting transmission and reception of the RF test signals.Collectively, these coefficients h define the channel condition numberk(H), which is the product of the norm of the H matrix and the norm ofthe inverse of the H matrix, as represented by the following equation:k(H)∥H∥*∥H ⁻¹∥

The factors affecting these coefficients can alter the channel conditionnumber in ways that can create measurement errors. For example, in apoorly conditioned channel, small errors can cause large errors in thetesting results. Where the channel number is low, small errors in thechannel can produce small measurements at the receive (RX) antenna.However, where the channel number is high, small errors in the channelcan cause large measurement errors at the receive antenna. This channelcondition number k(H) is also sensitive to the physical positioning andorientation of the DUT within its testing environment (e.g., a shieldedenclosure) and the orientation of its various antennas 204. Accordingly,even if with no extraneous interfering signals originating elsewhere orarriving via reflections and impinging on the receive antennas 204, thelikelihood of repeatable accurate test results will be low.

Referring to FIG. 5, in accordance with one or more exemplaryembodiments, the test signal interface between the tester 100 a and DUT200 a can be wireless. The DUT 200 a is placed within the interior 301of a shielded enclosure 300. Such shielded enclosure 300 can beimplemented as a metallic enclosure, e.g., similar in construction or atleast in effect to a Faraday cage. This isolates the DUT 200 a fromradiated signals originating from the exterior region 302 of theenclosure 300. In accordance with exemplary embodiments, the geometry ofthe enclosure 300 is such that it functions as a closed-ended waveguide.

Elsewhere, e.g., disposed within or on an opposing interior surface 302of the enclosure 300, are multiple (n) antennas arrays 102 a, 102 b, . .. , 102 n, each of which radiates multiple phase-controlled RF testsignals 103 a, 103 b, . . . , 103 n (discussed in more detail below)originating from the test signal sources 110 a, 110 b, . . . , 110 nwithin the tester 100 a. Each antenna array includes multiple (M)antenna elements. For example, the first antenna array 102 a includes mantenna elements 102 aa, 102 ab, . . . 102 am. Each of these antennaelements 102 aa, 102 ab, . . . , 102 am is driven by a respectivephase-controlled RF test signal 131 aa, 131 ab, . . . , 131 am providedby respective RF signal control circuitry 130 a.

As depicted in the example of the first RF signal control circuitry 130a, the RF test signal 111 a from the first RF test signal source 110 ahas its magnitude increased (e.g., amplified) or decreased (e.g.,attenuated) by signal magnitude control circuitry 132. The resultingmagnitude-controlled test signal 133 is replicated by signal replicationcircuitry 134 (e.g., a signal divider). The resultingmagnitude-controlled, replicated RF test signals 135 a, 135 b, . . . ,135 m have their respective signal phases controlled (e.g., shifted) byrespective phase control circuits 136 a, 136 b, . . . , 136 m to producemagnitude- and phase-controlled signals 131 aa, 131 ab, . . . , 131 amto drive the antenna elements 102 aa, 102 ab, . . . , 102 am of theantenna array 102 a.

The remaining antenna arrays 102 b, . . . , 102 n and their respectiveantenna elements are driven in a similar manner by corresponding RFsignal control circuits 130 b, . . . , 130 m. This producescorresponding numbers of composite radiated signals 103 a, 103 b, . . ., 103 n for conveyance to and reception by the antennas 202 a, 202 b, .. . , 202 n of the DUT 200 a in accordance with the channel H matrix, asdiscussed above. The DUT 200 a processes its corresponding received testsignals 211 a, 211 b, . . . , 211 m and provides one or more feedbacksignals 201 a indicative of the characteristics (e.g., magnitudes,relative phases, etc.) of these received signals. These feedback signals201 a are provided to control circuitry 138 within the RF signal controlcircuits 130. This control circuitry 138 provides control signals 137,139 a, 139 b, . . . , 139 m for the magnitude control circuitry 132 andphase control circuitry 136. Accordingly, a closed loop control path isprovided, thereby enabling gain and phase control of the individualradiated signals from the tester 100 a for reception by the DUT 200 a.(Alternatively, this control circuitry 130 can be included as part ofthe tester 100 a.)

In accordance with well-known channel optimization techniques, thecontrol circuitry 138 uses this feedback data 201 a from the DUT 200 ato achieve optimal channel conditions by altering the magnitudes andphases of the radiated signals in such a manner as to minimize thechannel condition number k(H), and produce received signals, as measuredat each DUT antenna 202, having approximately equal magnitudes. Thiswill create a communication channel through which the radiated signalsproduce test results substantially comparable to those produced usingconductive signal paths (e.g., RF signal cables).

This operation by the control circuitry 138 of the RF signal controlcircuitry 130, following successive transmissions and channel conditionfeedback events, will vary the signal magnitude and phase for eachantenna array 102 a, 102 b, . . . , 102 n to iteratively achieve anoptimized channel condition number k(H). Once such an optimized channelcondition number k(H) has been achieved, the corresponding magnitude andphase settings can be retained and the tester 100 a and DUT 200 a cancontinue thereafter in a sequence of tests, just as would be done in acabled testing environment.

In practice, a reference DUT can be placed in a test fixture within theshielded enclosure 300 for use in optimizing the channel conditionsthrough the iterative process discussed above. Thereafter, further DUTsof the same design can be successively tested without having to executechannel optimization in every instance, since differences in path lossexperienced in the controlled channel environment of the enclosure 300should be well within normal testing tolerances.

Referring still to FIG. 5, for example, an initial transmission wasmodeled to produce a channel condition number of 13.8 db, and themagnitudes of the h₁₁ and h₂₂ coefficients were −28 db and −28.5 db,respectively. The magnitude matrix for the channel H would berepresented as follows:

${H\;{dB}} = \begin{bmatrix}{- 28} & {- 34.2} \\{- 29.8} & {- 28.5}\end{bmatrix}$ k(H) = 13.8  dB

After iterative adjustments of magnitude and phase, as discussed above,the channel condition number k(H) was reduced to 2.27 db, and theamplitudes of the h₁₁ and h₂₂ coefficients were −0.12 db and −0.18 db,respectively, producing a channel magnitude matrix as follows:

$H_{dB} = \begin{bmatrix}{- 0.12} & {- 13.68} \\{- 15.62} & {- 0.18}\end{bmatrix}$ k(H) = 2.27  dB

These results are comparable to those of a cabled testing environment,thereby indicating that such a wireless testing environment can providetest results of comparable accuracy. By eliminating time for connectingand disconnecting cabled signal paths, and factoring in the reduced timefor gain and phase adjustments, the overall received signal test time issignificantly reduced.

Referring to FIG. 6, influences of multipath signal effects upon thechannel condition can be better understood. As discussed above, oncedisposed within the interior 301 of the enclosure 300, the DUT 200 a,during transmit testing, radiates an electromagnetic signal 203 a fromeach antenna 202 a. This signal 203 a includes components 203 b, 203 cthat radiate outwardly and away from the antenna 102 a of the tester 100a. However, these signal components 203 b, 203 c are reflected off ofinterior surfaces 304, 306 of the enclosure 300 and arrive as reflectedsignal components 203 br, 203 cr to combine, constructively ordestructively, depending upon the multipath signal conditions, with themain incident signal component 203 ai. As discussed above, dependingupon the constructive and destructive nature of the interference, testresults will generally tend to be unreliable and inaccurate for use inproper calibration and performance verification.

Referring to FIG. 7, in accordance with an exemplary embodiment, RFabsorbent materials 320 a, 320 b are disposed at the reflective surfaces304, 306. As a result, the reflected signal components 203 br, 203 crare attenuated significantly, thereby producing less interference,either constructively or destructively, with the incident primary signalcomponent 203 ai.

Additional RF signal control circuitry 150 can be included for usebetween the antenna array 102 a mounted within the interior 301 or onthe interior surface 302 of the enclosure 300 a and the tester 100 a.(Alternatively, this additional control circuitry 150 can be included aspart of the tester 100 a.) The radiated signals impinging upon theantenna elements 102 aa, 102 ab, . . . , 102 am produce received signals103 aa, 103 ab, . . . , 103 am with respective signal phases controlled(e.g., shifted) by phase control circuitry 152 having phase controlelements 152 a, 152 b, . . . , 152 m controlled in accordance with oneor more phase control signals 157 a, 157 b, . . . , 157 m provided by acontrol system 156. The resulting phase-controlled signals 153 arecombined in a signal combiner 154 to provide the received signal 155 afor the tester 100 a and a feedback signal 155 b for the control system156. The control system 156 processes this feedback signal 155 b, aspart of a closed loop control network, to adjust, as needed, therespective phases of the composite receive signals 103 aa, 103 ab, . . ., 103 am to minimize the apparent signal path loss associated with theinterior region 301 of the enclosure 300 a. This closed loop controlnetwork also allows the system to reconfigure the phased array enabledby these antennas 102 a and phase control circuitry 152 in the eventthat the positioning or orientation of the DUT 200 a changes within theenclosure 300 a. As a result, following minimization of the path lossusing this feedback loop, accurate and repeatable conveyance of the DUTsignal 203 a to the tester 100 a using the radiated signal environmentwithin the enclosure 300 a can be achieved.

Referring to FIG. 8, similar control and improvement in producingaccurate and repeatable test results can be achieved for DUT receivesignal testing. In this case, the test signal 111 a provided by thetester 100 a is replicated by the signal combiner/splitter 154, and therespective phases of the replicated test signals 153 are adjusted asnecessary by the phase control circuitry 152 before being radiated bythe antenna elements 102 aa, 102 ab, . . . , 102 am. As in the previouscase, the reflected signal components 103 br, 103 cr are significantlyattenuated and result in reduced constructive and destructiveinterference with the primary incident signal component 103 ai. One ormore feedback signals 203 a from the DUT 200 a provide the controlsystem 156 with the information necessary for controlling the phases ofthe replicated test signals 153 to minimize the apparent signal pathloss associated with the interior 301 of the enclosure 300 a, therebyestablishing consistent and repeatable signal path loss conditions.

Referring to FIG. 9, in accordance with one or more exemplaryembodiments, the shielded enclosure 300 b can be implementedsubstantially as shown. As discussed above, the DUT can be positioned atone end 301 d of the interior 301 of the enclosure 300 b, opposite ofthe interior region 301 b containing or facing the interior surface 302on which the tester antenna arrays 102 a, 102 b, . . . , 102 n (FIG. 5)are located. In between is an interior region 301 a forming a waveguidecavity surrounded by the RF absorbent materials 320.

As discussed above and in more detail below, exemplary embodiments ofsystems and methods enable cable-free testing of wireless DUTs whilecompensating for multipath effects and optimizing control of signal pathlosses. Multiple antennas, as well as antenna arrays, used inconjunction with control systems allow for adjustment of the phases ofthe test signals provided to the antenna elements in such a manner as toemulate the stable and repeatable signal path loss environment normallyassociated with a conductive signal path environment, while using aradiated signal environment within a shielded enclosure. While the timeneeded for adjusting the phase shifters is part of the overall testtime, such adjustment time is significantly less than that needed forconnecting and disconnecting test cables and provides the added benefitof real world testing that includes the antenna elements.

Further, as discussed in more detail below, exemplary embodimentsprovide for cable-free testing of wireless DUTs while achieving testingaccuracies and repeatable measurements commensurate with testing usingconductive signal paths, e.g., test cables, for signals having a widebandwidth, such as the 160 megahertz (MHz) wide signal as prescribed bythe Institute of Electrical and Electronic Engineers (IEEE) standard802.11ac. By adjusting the phases of the test signals provided to theantenna elements, a substantially flat signal response can be createdfor the wideband signal being received within the shielded testenclosure. Once the individual test signal phases driving the individualantenna elements have been adjusted to create such a flat signalresponse environment, the testing using the wideband signal may proceedwithout further adjustment, just as though it were in a cabled testenvironment. While positioning of the DUT within the shielded enclosurecan affect the flatness of the channel response, such positioningsensitivity has been found to be well within the tolerance ofmeasurements prescribed by underlying signal standards (e.g., IEEE802.11ac).

Further still, in accordance with exemplary embodiments, such cable-freetesting can be performed upon multiple DUTs simultaneously within thesame shielded enclosure. With appropriate control and adjustments of thephases and magnitudes of the test signals driving the multiple antennaelements, the low crosstalk signal environment of conductive signalpaths can be emulated using a radiated test signal environment within ashielded enclosure. Once the phases and gains (or attenuations) of thetest signals driving the antenna elements have been adjusted inaccordance with the exemplary embodiments, the signals received at theantennas of the multiple DUTs will be commensurate with signals receivedusing cabled signal paths. For example, this can be achieved bymaximizing the direct-coupled coefficients while minimizing thecross-coupled coefficients of the channel matrix (e.g., producingdifferences of at least 10 decibels between the direct- andcross-coupled coefficients).

Referring to FIG. 10, in accordance with exemplary embodiments, a DUT200 a is positioned within the shielded enclosure 300 for transmitsignal testing. The DUT test signal 203 a, transmitted via its antenna202 a, is received by the multiple antenna elements 102 a, 102 b, . . ., 102 n. The resulting received signals 105 a, 105 b, . . . , 105 n havetheir respective signal phases controlled and adjusted by respectivephase control circuits 236 a, 236 b, . . . , 236 n.

In accordance with some exemplary embodiments, the resultingphase-controlled test signals 237 a, 237 b, . . . , 237 n are conveyedto a control system 242 (discussed in more detail below) and signalcombining circuitry 234. The control system 242 provides phase controlsignals 243 a, 243 b, . . . , 243 n for the phase control circuits 236a, 236 b, . . . , 236 n. The combined (e.g., summed) phase-controlledtest signals 237 a, 237 b, . . . , 237 n produce a composite test signal235 for downstream analysis, e.g., by a VSA (not shown).

In accordance with other embodiments, the phase-controlled test signals237 a, 237 b, . . . , 237 n are combined in the signal combiner 234 toproduce the composite test signal 235. The composite test signal 235 isconveyed to an alternative control system 244 (discussed in more detailbelow), which, in turn, provides the phase control signals 245 a, 245 b,. . . , 245 n for the phase control circuits 236 a, 236 b, . . . , 236n.

Referring to FIG. 11, in accordance with one exemplary embodiment, thein-line control system 242 includes power measurement circuits 242 aa,242 ab, . . . , 242 an for measuring respective power levels of thephase-controlled test signals 237 a, 237 b, . . . , 237 n. The resultingpower measurement signals 243 aa, 243 ab, . . . , 243 an, indicative ofthe respective test signal power levels, are provided to controlcircuitry 242 b, e.g., in the form of a digital signal processor (DSP),which, in turn, provides appropriate phase control signals 243 ba, 243bb, . . . , 243 bn for the phase control circuits 236 a, 236 b, . . . ,236 n.

Referring to FIG. 12, in accordance with an exemplary embodiment,operation 410 of the testing environment of FIG. 11 can proceed asshown. First, the phase shifters 236 a, 236 b, . . . , 236 n areinitialized 411, e.g. where all phase shift values are set to a commonreference phase value or individual reference phase values. Next, thepower levels of the phase-controlled signals, 237 a, 237 b, . . . , 237n are measured 412. Next, the measured power values are summed 413 andthe cumulative measured signal power is compared 414 to a previouscumulative measured signal power. If the current cumulative measuredpower is greater than the previous cumulative measured power, thecurrent phase shift values and cumulative measured power are stored 415,following which, these stored values are compared 416 against thedesired criteria (e.g., a maximized cumulative measured power). If suchcriteria are met, adjustments of the test signal phases are terminated417. If not, adjustments of the test signal phases continue.

Similarly, if the current cumulative measured power is not greater thanthe previous cumulative measured power 414, adjustments of the testsignal continue. Accordingly, the phase shifters 236 a, 236 b, . . . ,236 n are adjusted 418 to impart another combination or permutation ofphase shift values upon the received test signals 105 a, 105 b, . . . ,105 n, e.g., in accordance with a genetic algorithm (GA) or a particleswarm algorithm (PSA). Following this, the measuring 412, summing 413and comparing 414 of powers are repeated until the desired criteria havebeen met.

Referring to FIG. 13, in accordance with another exemplary embodiment,the alternative downstream control system 244 (FIG. 10) includes powermeasurement circuitry 244 a (e.g., a VSA) and control circuitry 244 b(e.g., a DSP). A power level of the composite signal 235 is measured bythe power measurement circuitry 244 a, which provides power measurementdata 245 a to the control circuitry 244 b. In turn, the controlcircuitry 244 b provides appropriate phase control signals 245 ba, 245bb, . . . , 245 bn to the phase shifters 236 a, 236 b, . . . , 236 n.

Referring to FIG. 14, operation 420 of the testing environment of FIG.13 can proceed as shown. First, the phase shifters 236 a, 236 b, . . . ,236 n are initialized 421, by being preset to one or more respectivephase shift values. Next, the power level of the composite signal 235 ismeasured 422, following which, the current measured power is compared423 to a previous measured power level. If the current measured powerlevel is greater than the previous measured power level, the currentphase shift values and measured power are stored 424 and used fordetermining 425 whether the desired criteria (e.g., a maximized measuredpower level) have been met. If so, phase adjustments are terminated 426.If not, phase adjustments continue.

Similarly, if the current measured power is not greater than theprevious measured power, phase adjustments continue. Accordingly, thephase shifters 236 a, 236 b, . . . , 236 n are adjusted to impartanother set of phase shift values upon the received test signals 105 a,105 b, . . . , 105 n in accordance with an optimization algorithm (e.g.,a GA or PSA).

Referring to FIG. 15, in accordance with another exemplary embodiment,the in-line control system 242 (FIG. 10) includes phase detectioncircuits 242 ca, 242 cb, . . . , 242 cn and control circuitry 242 d(e.g., a DSP). The phase detectors 242 ca, 242 cb, . . . , 242 cn detectthe respective signal phases of the phase-controlled signals 237 a, 237b, . . . , 237 n, and provide corresponding phase data 243 ca, 243 cb, .. . , 243 cn to the control circuitry 242 d. Based upon this data, thecontrol circuitry 242 d provides appropriate phase control signals 243da, 243 db, . . . , 243 dn for the phase shifters 236 a, 236 b, . . . ,236 n.

Referring to FIG. 16, operation 430 of the testing environment of FIG.15 can proceed as shown. First, the phase shifters 236 a, 236 b . . . ,236 n are initialized 431 by being present to one or more respectivephase shift values. Next, the respective phases of the phase-controlledsignals 237 a, 237 b, . . . , 237 n are measured 432 (e.g., relative toa common or reference signal phase).

Next, based upon the measured test signal phases, the phase adjustmentsof the phase shifters 236 a, 236 b . . . , 236 n are configured 433 inaccordance with optimized phase shift values. Following this, the powerlevel of the composite signal 235 is measured 434 to confirm itsattainment of the desired composite signal power level, following whichphase adjustments are terminated 435.

Referring the FIG. 17, an exemplary received signal 203 radiated from aDUT 200 a with constant power from a wideband antenna 202 a with goodresponse for frequencies ranging from 700 through 6000 MHz within ashielded enclosure 300 (e.g., FIG. 6) would appear substantially asshown. As will be readily appreciated, its power profile will not beflat due to the rich multipath signal environment existing within theshielded enclosure 300. In the case of a packet data signal communicatedin accordance with IEEE standard 802.11ac, of particular interest is the160 MHz wide frequency band from 5000 through 5160 MHz. As can be seen,within this frequency band 511, as seen in the expanded portion 510 ofthe signal 203 profile, the received signal displays a power variationof approximately 25 decibels (dB). In accordance with exemplaryembodiments, using testing environments such as those discussed above,with multiple phase shifters for controlling the phases of the testsignals driving the multiple antenna elements, this profile can becompensated so as to become substantially flat over the frequency band511 of interest.

Referring to FIG. 18, in accordance with one exemplary embodiment, thiscan be achieved using multiple (e.g., 16) antenna elements 102 andcorresponding phase shifters 236. For example, using an optimizationalgorithm (discussed in more detail below), and using only quadraturephase adjustments of 0, 90, 180 and 270 degrees, it is possible toachieve an optimally flat response condition 523. As can be seen, priorto compensation, the response profile 522 varies more than 5 dB over the160 MHz bandwidth 511 of this exemplary test signal. Further, even whenthe antenna array is optimized for power level at the frequency midpointof 5080 MHz, as shown in the upper profile 521, received signalvariation is still approximately 5 dB. But when the multiple phaseadjusters 236 a, 236 b, . . . , 236 p are appropriately adjusted, eventhough confined to quadrature phase adjustments only, it is possible toachieve a response profile 523 that varies no more than 0.5 dB.

Referring to FIG. 19, the compensation has depicted in FIG. 18 can beachieved using a process 440 as shown. First, a number of frequencieswithin the desired signal bandwidth are defined 441, following which aninitial set of phase shift values for the phase shifters is defined 442.The phase shifters are then set 443 with such defined phase values andthe power is measured 444 at each frequency. Next, differences betweenmeasured powers at multiple pairs of the defined frequencies arecomputed 445 and summed for evaluation of 446 a function F equal to adifference between a defined maximum power difference and the summeddifferences of computed powers.

If the current computed function F_(current) is greater than a formercomputed function F_(old), then the phase shifter values are retained448 and it is determined 449 whether a desired condition has been met(e.g., a maximized computed function F has been attained). If so, phaseadjustments are terminated 450. If not, phase adjustments continue.Similarly, if the current computed function F_(current) is not greaterthan a former computed function F_(old), phase adjustments continue.These phase adjustments continue by defining another set of phaseshifter values 451 and repeating the steps of adjusting the phases 443,measuring power 444, computing power differences 445 and evaluating thecomputed function F 446. This process is repeated until the conditionhas been met 449.

Referring to FIG. 20, in accordance with exemplary embodiments, similarcompensation can be achieved in the context of cross-coupled signalswithin a shielded enclosure 300 when performing cable-free testing ofmultiple wireless DUTs. (For purposes of this example, two DUTs 200 a,200 b are to be tested using two antenna arrays 235 a, 235 b. However,it will be readily appreciated that other numbers of DUTs and antennaarrays can be used as well. Further, it will be readily appreciated thatwhat are depicted here as separate “DUTs” 200 a, 200 b may be respectivereceivers within a single MIMO DUT 200.) As discussed above, signalsources (e.g., VSGs) 110 provide test signals 111 which are replicatedusing signal splitters 234 to provide replica test signals 235 for phaseshifting using multiple phase shifters 231 for driving the antennaelements 102 of the antenna arrays 235. These antenna arrays 235 a, 235b provide radiated signal components 103 aa, 103 ab, 103 ba, 103 bbcorresponding to the direct-coupled and cross-coupled coefficients ofthe channel matrix H (e.g., as discussed above). These signal components103 aa, 103 ab, 103 ba, 103 bb are received by the antennas 202 a, 202 bof the DUTs 200 a, 200 b. Received signal data 201 a, 201 b are providedby the DUTs 200 a, 200 b to a control system 206 (e.g., a DSP), which,in turn, provides appropriate phase control signals 207 ap, 207 bp forthe phase shifters 236 aa, . . . , 236 am, 236 ba, . . . , 236 bm forcontrolling the phases of the signals to be radiated from the antennaelements 102 aa, . . . , 102 am, 102 ba, . . . 102 bm of the antennaarrays 235 a, 235 b.

By iteratively adjusting the phases of the radiated signals, asdiscussed above, the direct-coupled channel matrix H coefficients 103aa, 103 ba can be maximized and the cross-coupled coefficients 103 ab,103 bb minimized (e.g., with the final cross-coupled coefficientsideally becoming more than 10 dB less than the direct-coupledcoefficients).

Referring to FIG. 21, in accordance with another exemplary embodiment,the control system 206 can be further configured to provide gain controlsignals 207 ag, 207 bg for controlling the magnitudes of the testsignals 111 a, 111 b being replicated for transmission to the DUTs 200a, 200 b. These signal magnitudes can be controlled by controllingsignal gain stages (e.g., variable gain amplifiers or signalattenuators) 232 a, 232 b. This can beneficially provide for furtheroptimizing the relative magnitudes of the direct-coupled coefficients103 aa, 103 ba and cross-coupled coefficients 103 ab, 103 bb of thechannel matrix H. For example, the magnitudes of the direct-coupledcoefficients 103 aa, 103 ba can be normalized, while still maintainingsufficient attenuation of the cross-coupled coefficients 103 ab, 103 bb(e.g., 10 dB or more).

Various other modifications and alterations in the structure and methodof operation of this invention will be apparent to those skilled in theart without departing from the scope and the spirit of the invention.Although the invention has been described in connection with specificpreferred embodiments, it should be understood that the invention asclaimed should not be unduly limited to such specific embodiments. It isintended that the following claims define the scope of the presentinvention and that structures and methods within the scope of theseclaims and their equivalents be covered thereby.

What is claimed is:
 1. A method of facilitating wireless testing of aplurality of radio frequency (RF) signal transceiver devices under test(DUTs), comprising: providing at least first and second wired RF testsignals having corresponding at least first and second wired RF testsignal phases; controlling said at least first and second wired RF testsignal phases to provide corresponding at least first and secondcontrolled RF signals; transmitting, via a plurality of antennasdisposed at least partially within an interior region of a structure,said at least first and second controlled RF signals for reception by atleast first and second DUTs, respectively, disposed within said interiorregion, wherein said structure defines said interior region and anexterior region, and is configured to substantially isolate saidinterior region from electromagnetic radiation originating from saidexterior region; receiving corresponding at least first and secondsignals from said at least first and second DUTs indicative,respectively, of at least as received by said first DUT, a first powerlevel of one or more signals related to said first controlled RF signaland a second power level of one or more signals not related to saidfirst controlled RF signal, and as received by said second DUT, a thirdpower level of one or more signals related to said second controlled RFsignal and a fourth power level of one or more signals not related tosaid second controlled RF signal; and repeating said controlling of saidat least first and second wired RF test signal phases until said firstand third power levels exceed said third and fourth power levels by aminimum amount.
 2. The method of claim 1, wherein: said at least firstand second wired RF test signals further have corresponding at leastfirst and second wired RF test signal magnitudes; and said methodfurther comprises controlling said at least first and second wired RFtest signal magnitudes to provide said corresponding at least first andsecond controlled RF signals, and repeating said controlling of said atleast first and second wired RF test signal magnitudes until said firstand third power levels are approximately equal.
 3. A method offacilitating wireless testing of a plurality of radio frequency (RF)signal transceiver devices under test (DUTs), comprising: providing atleast first and second wired RF test signals having corresponding atleast first and second wired RF test signal phases; controlling said atleast first and second wired RF test signal phases to providecorresponding at least first and second controlled RF signals;transmitting, via a plurality of antennas disposed at least partiallywithin an interior region of a structure, said at least first and secondcontrolled RF signals for reception by at least first and second DUTs,respectively, disposed within said interior region, wherein saidstructure defines said interior region and an exterior region, and isconfigured to substantially isolate said interior region fromelectromagnetic radiation originating from said exterior region, andsaid plurality of antennas and at least a portion of said interiorregion together define at least a portion of a wireless communicationchannel via which at least first and second pluralities of controlled RFsignal components related to said at least first and second controlledRF signals, respectively, propagate for reception by said at least firstand second DUTs, respectively; receiving corresponding at least firstand second signals from said at least first and second DUTs indicative,respectively, of at least as received by said first DUT, a first powerlevel of said first plurality of controlled RF signal components and asecond power level of a plurality of controlled RF signal componentsother than said first plurality of controlled RF signal components, andas received by said second DUT, a third power level of said secondplurality of controlled RF signal components and a fourth power level ofanother plurality of controlled RF signal components other than saidsecond plurality of controlled RF signal components; and repeating saidcontrolling of said at least first and second wired RF test signalphases until said first and third power levels exceed said third andfourth power levels by a minimum amount.
 4. The method of claim 3,wherein: said at least first and second wired RF test signals furtherhave corresponding at least first and second wired RF test signalmagnitudes; and said method further comprises controlling said at leastfirst and second wired RF test signal magnitudes to provide saidcorresponding at least first and second controlled RF signals, andrepeating said controlling of said at least first and second wired RFtest signal magnitudes until said first and third power levels areapproximately equal.
 5. A method of facilitating wireless testing of aplurality of radio frequency (RF) signal transceiver devices under test(DUTs), comprising: providing at least first and second wired RF testsignals having corresponding at least first and second wired RF testsignal phases; controlling said at least first and second wired RF testsignal phases to provide corresponding at least first and secondcontrolled RF signals; transmitting, via a plurality of antennasdisposed at least partially within an interior region of a structure,said at least first and second controlled RF signals for reception by atleast first and second DUTs disposed within said interior region,wherein said structure defines said interior region and an exteriorregion, and is configured to substantially isolate said interior regionfrom electromagnetic radiation originating from said exterior region,and said plurality of antennas and at least a portion of said interiorregion together define at least a portion of a wireless communicationchannel characterized by a wireless communication channel matrix Hhaving a plurality of wireless communication channel coefficientsh_(ij), including direct-coupled coefficients, where i=j, andcross-coupled coefficients, where i≠j; receiving corresponding at leastfirst and second signals from said at least first and second DUTsindicative of corresponding at least first and second power levels ofsaid at least first and second controlled RF signals received by said atleast first and second DUTs and related to said plurality of wirelesscommunication channel coefficients; and repeating said controlling ofsaid at least first and second wired RF test signal phases until saiddirect-coupled coefficients are greater than said cross-coupledcoefficients by a minimum amount.
 6. The method of claim 5, wherein:said at least first and second wired RF test signals further havecorresponding at least first and second wired RF test signal magnitudes;and said method further comprises controlling said at least first andsecond wired RF test signal magnitudes to provide said corresponding atleast first and second controlled RF signals, and repeating saidcontrolling of said at least first and second wired RF test signalmagnitudes until said direct-coupled coefficients are approximatelyequal.